Muon's magnetic moment exposes a hole in the Standard Model, unless it doesn't
physicsworld.com
physicsworld.com
a bit unsatisfying, basically the Muon g-2 Theory Initiative which gave us the 2020 prediction that turned out to be wildly different from FNAL measurement is going to publish an updated version of the prediction after FNAL releases their final result.
it means the Theory Initiative will have a target that will never move to aim for when working out their final SM prediction
Sure, and this breaks some level of independence between this two workstreams -- it seems unlikely that the Theory Initiative will publish a number that diverges further from the experimental side.
But on the other hand, we're going to be in a world where there are two theoretical estimates, one based partially on empirical methods and one based on lattice methods, and these are going to diverge. So the obvious next task for the theory group is to (a) explain why these diverge and (b) explain why the lattice method is the more accurate one. Which likely will lead to more work for the experimentalists to explain why the inputs to the empirical methods didn't generalize.
Plenty to still learn here.
FermiLab is doing some great amazing work.
We have references: https://cerncourier.com/a/new-muon-g-2-result-bolsters-earli...
Our universe is a subtle mess.
This article was a lot clearer for me
The data-driven approach yields an accurate SM prediction, but the universe and lattice methods agree on a "bad" SM result, due to an undiscovered fact about measure theory and the correct interpretation of path integrals that the implementations of lattice QCD accidentally get right. Since the limit taken by lattice methods have never been proven to equal what we think the right interpretation of path integrals should be, the former could be right when the latter is erroneous.
Lattice QCD methods are definitely proven to be equivalent to the continuum theory when you take the appropriate limits. This isn't some mathematical mystery - Wilson's groundbreaking work in the 70s established this, and it's been rigorously developed since.
The actual g-2 puzzle is much more straightforward: we have competing measurements from different sources:
1. The Fermilab Muon g-2 experiment in Illinois directly measured the muon's anomalous magnetic moment.
2. The "data-driven" prediction used e+e- collision measurements from various experiments (BaBar at SLAC, KLOE in Italy, etc.) to calculate what the Standard Model predicts for g-2. This initially disagreed with Fermilab's measurement.
3. Lattice QCD calculations (like those from the BMW collaboration) produced theoretical predictions that matched Fermilab's experimental result.
4. More recently, new e+e- measurements from the CMD-3 experiment at VEPP-2000 in Russia (2023) are bringing the data-driven approach closer to both the lattice calculations and Fermilab's experimental values.
So it's really just a question of which experimental measurements of e+e- collisions are most accurate/resolve any experimental differences, not some exotic mathematical issue with QFT formulations.
https://azure.microsoft.com/en-us/blog/quantum/2025/02/19/mi...
Anyone know what are inside those tubes? Thinking to create this with a few younger ones and want to understand any risks should those tube breaks and something escapes.